This matter is before the court on a writ of error to review an order issued by the circuit court for Dodge County quashing a writ of habeas corpus.
Joseph E. Skinkis (petitioner) was convicted on his plea of guilty to a charge of first degree sexual assault in violation of sec. 940.225(1) (d), Stats. Petitioner alleges that the statute is unconstitutionally vague and void on its face because it fails to give adequate notice *531of the conduct it prohibits and lacks a “core” of meaning. The circuit court held that the statute was not unconstitutionally vague as applied to petitioner, and that it did give him adequate notice that his conduct was illegal.
I.
WAIVER
At the outset, the state contends that petitioner has waived his right to raise “any” constitutional challenge to the statute because he pleaded guilty to the charge. A number of recent Wisconsin cases lend initial credence to this argument, commencing with State v. Weidner, 47 Wis.2d 321, 177 N.W.2d 69 (1970). In that case, the court found that “as a general rule, the constitutionality of a statute cannot be questioned for the first time on appeal.” Id. at 323. The court noted the firmly established doctrine that a question of subject matter jurisdiction can never be waived, and therefore may be raised for the first time on appeal. Id., citing 4 C.J.S. Appeal & Error sec. 234, at 700-04 (1953). The court stated, however, at 324: “Ordinarily, a challenge to the constitutionality of a statute does not involve subject matter jurisdiction.”
The proposition that a defendant can waive the right to assert the unconstitutionality of the statute pursuant to which he is convicted by failing to make that claim at the trial court level has been repeated and expanded in three cases decided after Weidner. State v. Weso, 60 Wis. 2d 404, 210 N.W.2d 442 (1973) ; Flores v. State, 69 Wis. 2d 509, 230 N.W.2d 637 (1975) ; Cheatham v. State, 85 Wis.2d 112, 270 N.W.2d 194 (1978). This proposition is in apparent conflict with earlier Wisconsin and federal *532case law which holds that an unconstitutional statute is a nullity which can confer no jurisdiction whatsoever upon a court.1
These cases state the general rule as follows:
When a judgment of any court is based on an unconstitutional law it has no legitimate basis at all; it is not a judgment of a competent tribunal within the meaning of . . . the Statutes, or of a “competent court” within the meaning of those words in . . . the Statutes. The law, so called, being unconstitutional there is no law in fact, hence no jurisdiction to give force thereto; no legitimate jurisdiction over the subject matter or of the person, within the meaning of the decisions. Servonitz v. State, 133 Wis. 231, 236-37, 113 N.W. 277 (1907).
An unconstitutional law is void, and is as no law. An offense created by it is not a crime. A conviction under it is not merely erroneous, but is illegal and void and cannot be a legal cause of imprisonment. ... [I] f the laws [under which defendants were convicted] are unconstitutional and void, the circuit court acquired no jurisdiction of the causes. Its authority to indict and try the petitioners arose solely upon these laws. Ex Parte Siebold, 100 U.S. 371, 376-77 (1879).
An unconstitutional act of the legislature is not a law. It confers no rights, imposes no penalty, affords no protection, is not operative, and in legal contemplation has no existence. John F. Jelke Co. v. Beck, 208 Wis. 650, 661, 242 N.W. 576 (1932).
These cases have not been overruled, nor their holdings modified. They are not discussed or distinguished in *533Weidner,2 Weso,3 Flores4 or Cheatham.5 We have care*534fully examined the briefs filed in each of these four cases; in none of them were the earlier cases cited to the court.
The two lines of cases are difficult to reconcile. Weid-ner, and the cases which follow it, presume that ordinarily an attack on the constitutionality of a criminal statute does not go to subject matter jurisdiction. Servonitz, and the cases which follow it, presume that an constitutional attack on a statute raises a question of subject matter jurisdiction. The common ground between the two lines of cases is the unassailable proposition that an issue of subject matter jurisdiction cannot be waived by inadvertence or by deliberate failure to raise it at the trial court level, and that such an issue can always be raised as a matter of right for the first time on appeal or review by a higher court.6
*535As the Wisconsin Supreme Court held in Harrigan v. Gilchrist, 121 Wis. 127, 224, 99 N.W. 909 (1904), the court can and should reach an issue of subject matter jurisdiction even where neither party raises it.7
A challenge to the jurisdiction of the trial court of the subject matter of the action is proper at any time; and, without the question being urged by counsel. It is not only proper for this court, but it is its duty, to make all investigations necessary to satisfy itself in regard thereto with reasonable certainty.
Decisions of the United States Supreme Court are in accord with this familiar principle,8 and it was reasserted as recently as 1977 in Gelatt v. DeDakis, 77 Wis. 2d 578, 254 N.W.2d 171 (1977). There the court held that the appellant had waived his right to assert “most” of his objections to receivership proceedings by failing to raise them at trial, but that he could not waive his claim that the statutes under which the proceedings had been conducted were “suspended” by the Federal Bankruptcy Act and thus “ ‘utterly null and void’ ” under United States Supreme Court holdings. Id. at 584.
[I] t is fundamental that parties cannot confer subject matter jurisdiction upon a court by waiver or consent. . . . If Gelatt is correct in asserting that the receiver*536ship provisions of ch. 128 are suspended, and if the jurisdiction of the circuit court depended thereon, subject matter jurisdiction would be absent. To that extent Gelatt’s claims must be considered notwithstanding his participation in the receivership without complaint. 77 Wis. 578, 584-85.
In a footnote to the passage quoted above, the court distinguished Weidner, supra, as follows:
The fact that subject matter jurisdiction is at issue also renders inapplicable the rule that this court will not generally consider the constitutionality of a statute if raised for the first time on appeal. 77 Wis.2d 578, 585 n. 1.
The question before us, in light of all the above-cited case law, is whether the constitutional challenge asserted by this petitioner raises a question of subject matter jurisdiction. If it does not, he has waived his right to raise it for the first time on appeal; if it does, even his plea of guilty cannot waive it. A key for the resolution of this question is found in State ex rel. Comrs. of Pub. Lands v. Anderson, 56 Wis.2d 666, 203 N.W.2d 84 (1973), and In re Interest of F.R.W. (a minor), 61 Wis. 2d 193, 212 N.W.2d 130 (1973). In the former case, the court considered an equal protection challenge to a statute alleged to set forth arbitrary and unreasonable classifications in violation of the fourteenth amendment to the United States Constitution. In upholding the statute, the Wisconsin Supreme Court stated:
A statute, unconstitutional on its face, is void from its beginning to the end; but a statute unconstitutional in an application is only void as applied in a certain time and to the specific circumstances. 56 Wis.2d 666, 672.
This statement was quoted with approval in In re Interest of F.R.W., supra at 200, which involved a claim that former sec. 48.18, Stats., the juvenile court waiver stat*537ute, was void on its face for vagueness. The trial court in that case had found the statute unconstitutionally vague, and had dismissed a petition to waive the juvenile into adult court for that reason. On appeal of that determination, the initial question was whether the order dismissing that petition was appealable, and thus whether the supreme court had jurisdiction of the appeal. The then applicable appeals statute provided that an order was appealable if it decided a question of jurisdiction. In holding that the order was appealable the supreme court observed:
When the juvenile challenged the constitutionality of sec. 48.18, Stats., as being void for lack of standards, he was, in effect, arguing that the juvenile court had no jurisdiction to act pursuant to that section. The juvenile court judge’s determination that sec. 48.18 was unconstitutional was, in effect, a declaration that it had no jurisdiction to act pursuant to that section.
Since the juvenile court judge determined sec. 48.18 to be unconstitutional and void, it follows that she properly determined that she was without jurisdiction to act pursuant to the petition for waiver. 61 Wis.2d 193, 199-200.
Both State ex rel. Comrs. of Pub. Lands and F.R.W. recognize that there are different types of constitutional attacks on statutes, some of which, if successful, would render the particular statute at issue void and inoperable, and some of which would not have that drastic effect.9 *538F.R.W. recognizes that where a statute upon which the trial court’s power to act rests is alleged to be void and inoperable for vagueness on its face, the allegation raises a question of subject matter jurisdiction. Cheatham, supra, reasserts the fundamental principle that an issue of subject matter jurisdiction — arising from a claim that a statute upon which the trial court’s jurisdiction depends is inoperable for any reason. — can never be waived, and must be decided by the court even if not raised by the parties.
Although the court in Gelatt and F.R.W. did not expressly set forth a methodology for determining whether an attack (constitutional or otherwise) on a statute is an attack on the subject matter jurisdiction of the court, we deem its approach in those cases to be the proper procedure. In effect, the court considered the consequence of agreeing with the party asserting the statutory defect. In each case the court determined that if the attack on the statute were correct, the statute would be null and void and the court would be without the power to act under the statute. In this case, as in those cases, if this court were to agree with petitioner’s claim that the provisions of the sexual assault statute under which he was convicted are facially so vague as to lack a core of meaning, those statutory provisions would necessarily be declared void and inoperable, and no court would have power under them to convict the defendant for their violation. Servonitz v. State, 133 Wis. 231, 236-37, 113 N.W. 277 (1907), and see State v. Mahaney, 55 Wis.2d 443, 198 N.W.2d 373 (1972) ; State v. Starks, 51 Wis.2d 256, 186 N.W.2d 245 (1971).
Consequently, we hold that the issue raised by the petitioner in this case — that the provisions of the sexual *539assault act under whch he was convicted are void for facial vagueness — is an issue of subject matter jurisdiction which cannot be waived, and which this court has a duty to consider regardless of his guilty plea.
¡-H HH
VAGUENESS
Petitioner contends that the sexual assault act lacks a “core” of discernible meaning in that it fails to give notice of the conduct it prohibits and fails to provide standards for enforcement. Petitioner pleaded guilty to a criminal complaint alleging that he feloniously had sexual contact with a person under 12 years of age in violation of sec. 940.225(1) (d), Stats. The factual portion of the complaint alleges that petitioner, who was babysitting the 8 year old girl at the time of the incident, approached her from behind while she was in her bedroom and placed his hands on her vaginal area.
The legal effect of a plea of guilty is to admit the facts charged, but not the crime. State v. Pohlhammer, 78 Wis.2d 516, 523, 254 N.W.2d 478 (1977) ; State v. Lampe, 26 Wis.2d 646, 648, 133 N.W.2d 349 (1965). The initial question is whether the admitted facts fall within the “zone of prohibited conduct” so that no reasonable person could have doubt of their criminality. State v. Driscoll, 53 Wis.2d 699, 702, 193 N.W.2d 851 (1972). If they do, then petitioner will not be heard to raise by hypothetical example fact situations which might arguably be prosecuted under this act, and as to which the statute might be unconstitutionally vague. Butala v. State, 71 Wis.2d 569, 575, 239 N.W.2d 32 (1976) ; Jones v. State, 55 Wis.2d 742, 746, 200 N.W.2d 587 (1972) ; State v. Driscoll, 53 Wis.2d 699, 701-02. As the United *540States Supreme Court has held, “even if the outermost boundaries of [the statute] may be imprecise, any such uncertainty has little relevance . . . where appellants’ conduct falls squarely within the ‘hard core’ of the statute’s proscriptions.” Broadrick v. Oklahoma, 413 U.S. 601, 608 (1973). A person to whose conduct a penal statute clearly applies has no standing to attack the statute as vague and void on its face. Parker v. Levy, 417 U.S. 733, 756 (1974).
Section 940.225(1) (d), Stats., prohibits “sexual contact” with a person 12 years of age or younger. Section 940.225(5) (b) defines “sexual contact” in relevant part as follows:
the intentional touching by hand ... of the intimate parts, clothed or unclothed, of another, if that intentional touching can reasonably be construed as being for the purpose of sexual arousal or gratification ....
Section 940.225(5) (a) provides that “ ‘[ijntimate parts’ includes the breast, buttock, anus, penis, vagina or pubic mound of a human being.”
Petitioner contends that the statute lacks a core altogether and is thus void under the holding of Smith v. Goguen, 415 U.S. 566 (1974). In that case the defendant, who had worn pants with a small cloth copy of the American flag sewn on the seat, was convicted under a state statute punishing anyone who “treats contemptuously the flag of the United States.” Id. at 568-69. The court held:
This criminal provision is vague “not in the sense that it requires a person to conform his conduct to an imprecise but comprehensible normative standard, but rather in the sense that no standard of conduct is specified at all.” [Citation omitted.] Such a provision simply has no core. This absence of any ascertainable standard for inclusion and exclusion is precisely what offends the Due Process Clause. The deficiency is particularly ob*541jectionable in view of the unfettered latitude thereby accorded law enforcement officials and triers of fact. . . . The language at issue is void for vagueness as applied to Goguen because it subjected him to criminal liability under a standard so indefinite that police, court, and jury were free to react to nothing more than their own preferences for treatment of the flag. 415 U.S. 566, 578. (Emphasis in original.)
Petitioner argues that the sexual assault statute is similarly without a core, first, because the use of the word “includes” in the statutory definition of -intimate parts fails to exclude any part of the human body not specifically enumerated. He suggests that the statute might be used to prosecute a person who obtained sexual gratification by touching a foot, leg, arm, or other part of the human body.
Petitioner was not convicted of touching a foot or arm, but pleaded guilty to touching the vaginal area of a child. The statutory definition of intimate parts specifically includes the vagina of a human being. Petitioner is consequently without standing to raise the possibility that this statute might be used to prosecute the touching of unenumerated parts of the body. Smith v. Goguen does not support a contrary conclusion since the court in that case found the statute void as applied to the very act of which the defendant stood convicted, not to some hypothetical conduct.10
Petitioner also contends that the phrase “sexual arousal or gratification” provides no ascertainable standard of guilt unless the statute is construed to create a presumption that any touching of an “intimate part” is done for the purpose of sexual gratification or arousal. Without *542such a presumption, he reasons, the statute gives no notice to anyone of the kinds of touching it prohibits.11
We find no merit in this argument. The statute does not create a presumption. It prohibits the intentional touching of intimate parts “if that intentional touching can reasonably be construed as being for the purpose of sexual arousal or gratification.” By his plea of guilt, petitioner admitted the facts alleged in the complaint that he approached an 8 year old child from behind, while the child was in her bedroom, and intentionally placed his hands on her vaginal area. These are the only facts before us on review. As the circuit court noted, these facts do not suggest or admit of any other reasonable construction, standing alone, than that his act of touching was for the purpose specified in the statute.
The sexual statute has a core, and the admitted acts of the petitioner are within that core. This being so, we decline his invitation to speculate as to the perimeters of the conduct this statute prohibits by referring to hypothetical examples of behavior not presented by the facts before us. Smith v. Goguen and State v. Mahaney, supra, do not incline us to venture past the admitted facts, as both of those cases involved claims of over-breadth in the face of first amendment rights which are not asserted in this case. Where, as here, the claim of unconstitutionality is grounded on facial vagueness, and first amendment rights are not involved, the defendant “will not be heard to hypothesize other factual situations which might raise a question as to the applicability of *543the statute,” but is limited to the conduct actually charged in the complaint. State v. Courtney, 74 Wis.2d 705, 713, 247 N.W.2d 714 (1976).
By the Court. — Order affirmed.